Surge protector with input transformer

ABSTRACT

A surge protector for alternating current service includes at least an incoming hot line and a neutral line, but usually includes an incoming hot line, an incoming neutral line and a safety ground line. The surge protector has an input transformer and a series connected transformer with input connection to the input transformer secondary winding, and connected in series to a non-linear surge suppression circuit, and therefore has a gross output connection to the non-linear surge suppression circuit, and a low impedance input to the secondary winding of the series connected transformer from the non-linear surge suppression circuit, and has a surge cancelled hot line output connection.

REFERENCE TO RELATED APPLICATION

This application is a Continuation-In-Part of copending U.S. patentapplication Ser. No. 10/889,369, filed on Jul. 12, 2004, entitled “SURGEPROTECTOR”, by the same inventor herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to surge protection, and more particularlyto a surge protector that utilizes a non-linear surge suppressioncircuit with a series connected transformer, and includes an inputtransformer. This surge protector is useful for single phase service,and may be useful in three phase service applications wherein threetransformers (one for each hot line) are used. In the three phaseservice surge protector of the present invention canceling signals areadded by each transformer output.

2. Information Disclosure Statement

The following prior art is representative of the state of the art in thefield of surge protection:

U.S. Pat. No. 4,870,528 discloses a surge suppressor comprises a firstseries circuit having a first inductance and a first alternating voltagelimiter, including at least a first capacitance and a bi-directionallyconductive rectifying circuit for charging the first capacitance,coupled between first and second input terminals for limiting surgecurrents and voltage excursions coupled to first and second load outputterminals. The first alternating voltage limiter further comprises asensing circuit for sensing at least one of the charging currentsupplied to and the voltage developed across the first capacitance. Anauxiliary energy storage circuit and a normally open switching deviceresponsive to the sensing circuit are provided for coupling theauxiliary energy storage circuit across the first capacitance duringhigh energy surge conditions.

U.S. Pat. No. 4,870,534 discloses a surge suppressor for repeatedlyprotecting a load against surges occurring on A-C power mains fromlightning surges. It includes a first series circuit having a firstinductance and a first alternating voltage limiter, including at least afirst capacitance and a bidirectionally conductive rectifier circuit,coupled between first and second input terminals. The first inductanceconducts substantially all of the current supplied from the A-C powermains. A second series circuit comprising a second inductance and secondalternating voltage limiter, including at lest a second capacitance anda second bidirectionally conductive rectifier circuit, is coupled acrossthe first alternating voltage limiter and is coupled to first and secondoutput terminals. The first voltage excursions passed to the secondseries circuit to first levels while the second series circuit isarranged for further limiting surge currents and voltage excursionspassed to the output terminals to second levels less than first levels.

U.S. Pat. No. 5,617,284 discloses a power surge protection apparatusthat protects circuitry from electrical surges induced in an alternatingcurrent power connection to the circuity. The apparatus includes first,second, and third stages, which serve to clamp and dissipate superfluousenergy, such as that from a power surge, on the power connection. Thefirst stage comprises a metal oxide varistor MOV 1 and a capacitor forhelping to clamp and dissipate large-duration continuous surges on thepower connection. The second stage comprises an RC-LC filter withresistor R1, capacitor C2, inductor L1, and capacitor C3. Moreover, thesecond stage has a metal oxide varistor MOV 2. The second stage furthercomprises a bifilar transformer T1 situated between the connections.Specifically, the inductors of the bifilar transformer T1 are disposedin series with the connections of the power connection, and theconnections are twisted about each other and wrapped in a bifilarwinding configuration about a common core.

U.S. Pat. No. 5,621,625 discloses a surge protection circuit forswitching mode power supply utilizing the switching phase difference ofsubstantially 180 degree between primary and secondary coils of aswitching power supply transformer that snubs transformer by attenuatingthe surges induced during ON/OFF operations of a switching transistorwhich controls the power supply transformer. Accordingly, heat causedduring the ON/OFF operation of the switching transistor is reduced andsecondary rectifier diodes connected to the secondary winding of thepower transformer are protected from damages. The surge protectioncircuit uses a pair of capacitors connected in series between a controlterminal of the primary coil and an output terminal of the secondarycoil of the switching power supply transformer for snubbingbidirectional surges induced by the ON/OFF operation of the switchingtransistor.

United States Patent Application Disclosure No. 2003/0165035 A1describes a system and method for conditioning a power transmission,thereby eliminating adverse characteristics from the power transmission.The system selectively includes a voltage surge protector, and EMI/RFIfilter and at lest one inrush current suppressor integrally formed intoa single system. To condition an incoming power transmission, the powertransmission is passed through the voltage surge protector to eliminateany abnormal voltage spikes. The power transmission is then passedthrough an improved EMI/RFI filter having a dual output. The outputs ofthe EMI/RFI filter lead into a first inrush current suppressor. Theinrush current suppressor limits the amperage of the power transmissionfor a predetermined period of time and then permits unrestricted currentflow.

United States Patent Application Disclosure No. 2004/0004799 A1describes a surge suppression device includes a first and second coilpositioned in close proximity to one another such that the windings ofeach coil are disposed at an angle thereto. In a preferred embodiment,the coils are disposed such that the windings of each coil are placed ata right angle (90 degrees) to one another. However, angles of varyingdegree can be employed. Varying configurations of the coil windingplacement include a “sandwiched” type configuration, a “one on the topof the other” configuration as well as an intertwined configuration.Each embodiment employs additional surge elements such as metal oxidevaristors (MOVs). It is unnecessary to employ any ferrous material corefor any of the coils used in the novel device of the present invention.

Notwithstanding the prior art, the present invention is neither taughtnor rendered obvious thereby.

SUMMARY OF THE INVENTION

The present invention relates to a surge protector for a single phasealternating current service, and that service includes at least anincoming neutral line and incoming hot line, but usually includes anincoming hot line, an incoming neutral line and a safety ground line.The safety ground line is optional for the performance of the presentinvention surge protector but is now code required in all new structuresby many governnental bodies. The surge protector has an inputtransformer, with input connection means for connection to the incominghot line, followed by a series connected transformer connected in seriesto a non-linear surge suppression circuit, and therefore having a grossoutput connection to the non linear surge suppression circuit, andfurther having a low impedance input to the secondary winding of theseries connected transformer from the non-linear surge suppressioncircuit, and having a surge cancelled hot line output connection means.By “series connected transformer” as used herein means a seriesconnected conventional transformer (multiple windings) or anautotransformer (tapped winding). The present invention surge protectoralso has the non-linear surge suppression circuit having an inputconnection means from the single phase service neutral line, and isconnected with the gross output connection means of the transformer, andhas means for returning the suppressed surge signal to the transformersecondary which is wired in opposite phase, and having a neutral lineoutput connection means. The input transformer may be an isolationtransformer, a voltage step up transformer or a voltage step downtransformer. The non-linear surge suppression circuit starts to limitthe surge voltage at a voltage above the peak of the power wave voltage,and the series connected transformer senses the surge current. Thesecondary winding then supplies a signal of opposite phase to theincoming surge at the output after the clamping circuit, whicheffectively cancels the residual surge voltage, rendering the residualsurge benign at the output.

In many preferred embodiments, the surge protector is for a single phasealternating current service, the service including an incoming hot line,an incoming neutral line and a safety ground line wherein the devicefurther includes a three prong male alternating current plug at it'supstream end and a three slot female alternating current receptacle atit's downstream end.

The series connected transformer of the present invention surgeprotector has a primary winding and a secondary winding; an alternateconstruction would be a tap on the primary.

The present invention surge protector includes embodiments wherein threephase service is used in several configurations (wye, delta, grounded,ungrounded, etc.) The preferred configuration for use within buildingswill be described. In the present invention surge protector for threephase alternating current service, the preferred service configurationincludes three incoming hot lines designated phase A, phase B, and phaseC, a safety ground line, and a neutral line. The surge protector hasthree input transformers and three series connected transformers withinput connection means, one transformer connected to one non-linearsurge suppression circuit for each phase, with input connection meansfor connection to each phase, and each transformer primary is connectedin series to said non-linear surge suppression circuit. It therefore hasa gross output connection to the non-linear surge suppression circuit,and further has a low impedance input to the secondary winding of theseries connected transformer from the non-linear surge suppressioncircuit, and has a surge canceled output connection means for eachphase. It has the non-linear surge suppression having an inputconnection means from the three phase neutral wire (optionally the threephase ground wire), and being connected with the gross output connectionmeans of the transformer primary, having means for returning thesuppressed surge signal to the transformer secondary which is wired inopposite phase to provide a canceling signal, and having a ground lineand neutral line output connection means. Each non-linear surgesuppression circuit starts to limit the surge voltage at a voltage abovethe peak of the power wave voltage with respect to the neutral line (oroptionally the ground line), and the series connected transformerprimary senses the surge current and the secondary winding supplies asignal of opposite phase to the incoming surge at the output after theclamping circuit, which effectively cancels the residual surge voltage,rendering the residual surge benign at each output.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention should be more fully understood when thespecification herein is taken in conjunction with the drawings appendedhereto wherein:

FIGS. 1 through 6 are describing the present invention as claimed in theparent application to this application and are set forth in detail foran understanding of the basic concepts before introduction of thepresent invention input transformer, and FIGS. 7 and 8 illustrate thepresent invention with the input transformer, incorporating the featuresof the previously described drawings.

FIG. 1 illustrates a flow diagram of one embodiment of the presentinvention surge protector;

FIG. 2 shows a circuit diagram of one embodiment of a single phasepresent invention surge protector;

FIGS. 2A and 2B show alternate configurations where the use of theground line is permissible;

FIGS. 3 and 5 show waveform results for present invention surgeprotectors;

FIG. 4 shows a circuit diagram of a preferred embodiment of a singlephase present invention surge protector;

FIG. 4A shows an alternative non-linear surge suppression circuit forsome embodiments to substitute for that shown in FIG. 4;

FIG. 6 illustrates another embodiment of the present invention surgeprotector for three phase service;

FIG. 7 shows a circuit diagram of one embodiment of a single phasepresent invention surge protector; and,

FIG. 8 illustrates waveform results the present invention surgeprotector of FIG. 7 utilizing the non-linear surge suppression circuitof FIG. 4A.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Most electronic equipment is powered from “switch mode” power supplies.These power supplies generally take their power from the peak of thepower wave, making them particularly susceptible to powerline surgeswhich exceed the power wave peak voltage.

A powerline surge suppressor is described which, due to the phasecancellation property of a transformer connection, lets extremely littlesurge energy through to protected equipment, making it particularlyeffective for protecting such switch mode power supplies. The low surgeenergy let-through can be achieved by using a canceling signal from asecondary winding coupled from a transformer primary winding which isseries connected to the power line carrying the incoming surge. Byvirtue of the ability to select the phase of the secondary (canceling)winding, a canceling signal can be added in series with the outputfollowing the suppressing circuit, to produce exceptionally lowlet-through voltage.

Powerline surges within a building can be as large as 6,000 Volts, 3,000Amperes, with a duration of 50 microseconds, according to the industrystandard ANSI C62.41. UL uses 6,000 Volts, 500 Amps for their UL1449safety duty factor (endurance) testing, and for establishing theirstandard SVR (Suppressed Voltage Rating), and 6,000 volts, 3,000 ampsfor their Adjunct Classification (performance certification). Powerlinesurge suppressors should serve the purpose of reducing such electricalsurges to benign levels of voltage, current and duration (energy).

Most equipment today is powered from switch-mode power supplies. Thesesupplies take their power from the peak of the power wave, where theyoffer a very low impedance to the power wave during the peak period ofthe wave. This is important for understanding the following.

Two recent situations make conventional fixed voltage surge clampingproducts relatively ineffective in light of switch-mode power supplycharacteristics.

First, utility companies lower their powerline voltage during“brown-out” situations to conserve available electrical power. Thisvoltage may be 108 Volts RMS (152 Volts peak), or even lower. Sincefixed clamping level protection devices must be set to clamp at avoltage higher than the highest expected voltage (typically 10% abovenominal 120 volts) (132 volts RMS, or 187 Volts peak), plus the clampingcomponent tolerance, the typical clamping component is rated for 150Volts RMS (212 Volts peak). With a 10% tolerance, the clamping voltagewould range from 135 to 165 Volts RMS (190 to 233 Volts peak).

If the powerline Voltage is 108 Volts RMS (153 Volts peak), and thefixed clamping component is 165 Volts RMS (233 Volts peak), thenabsolutely no surge suppression takes place until after a surge voltageincrement of about 80 Volts peak! Such a large surge voltage incrementbefore any surge suppression even starts, can result in very largecurrents flowing into the “protected” power supply, damaging or puttingthese supplies under severe stress!

Second, during rolling blackouts, very large surges are created as themagnetic fields around all the current carrying wires collapse. Thesewide area regions of multiple surges put significant stress on powersupplies and surge components alike, making effective, reliablesuppression increasingly important.

The present invention surge protection has a circuit with thecharacteristic that it will effectively cancel the effects of a surge byproviding an opposing signal to the residual surge left after usingconventional suppression circuits and adding an opposing signal to theoutput, thereby dramatically reducing the surge voltage let through tothe protected equipment.

The present invention surge protection device has a circuit thatincludes an input transformer that may be an isolation transformer, astep up voltage transformer, or step down voltage transformer. Thesubsequent in-series connected conventional transformer can be reducedin size because the input transformer leakage inductance can substitutefor some or much of the otherwise needed inductance of the seriesconnected transformer. The input transformers used in the presentinvention devices can be constructed to handle wide ranges of power andhave predetermined transformer leakage inductance. An artisan in thefield has the skill to construct input transformers, given the presentinvention disclosure and identified power applications.

The present invention surge suppressor includes a transformer primarywinding connected in series with the “hot” wire, the input transformerand a non-linear surge suppression circuit. The series transformerprimary winding connection allows the transformer to be responsive tosurge current flowing in the surge suppression circuit, as all the surgecurrent flows in the primary winding.

The surge suppression circuit can consist of combinations of inductors,capacitors within a diode bridge, MOV's (Metal Oxide Varistors), gastubes, silicon diodes, silicon avalanche diodes (SADs) or any non-linearelement(s) suitable for surge suppression applications.

FIG. 1 illustrates a flow diagram of one embodiment of the presentinvention surge protector. Device 100 includes a series connectedtransformer 101 and a non-linear surge suppression circuit 103. There isincoming single phase alternating current service with hot-line 121,neutral line 123 and ground line 125. Series connected transformer 101is connected to incoming hot-line 121 (hard wired, conventional plug,clip or otherwise). In turn, series connected transformer 101 has agross output connection 105 to non-linear surge suppression circuit 103neutral line 123 is connected to non-linear surge suppression circuit,as shown. The non-linear surge suppression circuit 103 starts to limitthe surge voltage at a voltage above the peak of the power wave voltage.Non-linear surge suppression circuit 103 returns a surge suppressedsignal to series connected transformer secondary via a feedbackconnection 107, with the transformer secondary phased to cancel theresidual surge voltage. Thus, the device 100 senses the surge currentand supplies a signal of opposite phase to the suppressed surge,effectively canceling the residual surge voltage, rendering the residualsurge benign at hot line output 127.

The non-linear surge suppression circuit 103 may be any non-linear surgesuppression circuit such as I described above, using Metal OxideVaristors, SADs, or similar fixed clamping level surge suppressioncomponents. However, a preferred circuit uses dynamic clamping, wherebysurge suppression starts as soon as surge voltage exceeds the power wavepeak voltage. FIG. 4 a shows an example of a preferred dynamic clampingcircuit 410 that can be substituted for an MOV or similar clampingcomponent. FIG. 4 shows an example of typical implementation of thispreferred configuration 400, also described in more detail in my U.S.Pat. No. 6,728,089, entitled “Surge suppressor for wide range of inputvoltages.”

For fixed clamping elements such as MOVs and SADs, voltage clamping doesnot begin until the clamping onset voltage is exceeded. Since thisclamping onset level must be higher than the highest expected powerlinepeak voltage to prevent the suppressor from conducting on the power waveand overheating, the clamping onset level can be quite high, typically210 volts peak for 120 vac rms power. Additionally, the clamping is notperfect and the clamping voltage continues to rise past the clampingonset voltage as the surge current into the MOV increases due to theinternal resistance of the clamping circuit (3,000 amperes may flow inthe MOV or other clamp circuit would result in 300 volts in addition tothe initial 210 volts clamping onset voltage).

By preceding such a voltage clamping circuit with a series-connectedtransformer, the resulting overall surge let-through voltage can bereduced to benign levels by virtue of the current limiting properties ofthe series transformer inductance, and by adding the canceling signalfrom the series connected transformer secondary winding to the poweroutput connection after the voltage clamping circuit. The precisetransformer constants for optimum cancellation will depend on thespecific characteristics of the MOV or other clamping circuit.

A transformer (or autotransformer) suitable for sample 120 vac, 60 Hzapplications will have a normal coupling of 0.4 (normal coupling rangeof about 0.3 to 0.9, and a preferred normal coupling range of about 0.35to about 0.65) and the following unitized parameters: divide theunitized parameters supplied by the maximum rated load current for eachapplication:

Unitized Parameters:

-   Primary resistance: 0.6 ohms.-   Primary inductance: 1200 microhenries    The secondary will have the following unitized parameters:-   Resistance: 0.03 ohms.-   Inductance: 60 microhenries

Optimum overall performance will be achieved by optimizing the previousrecommended starting values in conjunction with the actual surgesuppressor components.

For example, a transformer for 120 VAC, 60 Hz, 20 Amperes maximum loadwould have the following parameters:

-   Primary resistance: 0.03 ohms.-   Primary inductance: 60 microhenries-   Secondary resistance: 0.0015 ohms.-   Secondary inductance: 3 microhenries.-   Nominal coupling: 0.5

The transformer inductance's and resistances can be doubled for 240 vac60 Hz applications, and scaled similarly for different voltages.

FIG. 2 shows the present invention surge suppressor circuit for aseries-connected transformer and 20 amp, 120 vac 60 Hz load. Thecomponents are as follows:

The single phase service 120 vac has a typical three line set up with ahot line, a neutral line, and a safety ground, access via conventionalthree prong plug is assumed for this example. Thus, the presentinvention device 200 has a three-prong male AC plug J201, basically, isa powerline plug for connecting to normal 120 vac 60 Hz power, althoughthe circuit could also be “hard wired” in a panel-mount application.

T201 is a transformer or autotransformer with a primary inductance of 60microhenries, DC resistance of 0.03 ohms, a secondary inductance of 3microhenries and a coefficient of coupling of 0.5. R201 is a secondarydamping resistor across the transformer secondary winding used to shapethe resulting voltage waveform to be consistent with the clampingcircuit response, in the range of 0.01 to 0.20 ohms. RV201 is a MetalOxide Varistor (MOV) or a similar clamping component with a nominalclamping onset level of 210 volts peak, typical of Varistors for usewith 120 vac power. As shown, it is wired consistent with FIG. 1 above.

MOVs and SADs (Silicon Avalanche Diodes) have similar clampingcharacteristics for RV201, but MOVs are sacrificial and wear out withuse, while SADs do not wear out up to their maximum rating, but aregenerally available with lower energy or power ratings. A more effectivecircuit would substitute the circuit of FIG. 4 a for RV201 in FIG. 2.

Since the neutral wire is tied to earth ground where the power enters abuilding for 120/240 vac systems as used in the USA, surges can onlyenter a building on the “hot” wires. The transformer (T201) primary istherefore connected between the incoming “hot” wire and the clampingcircuit (MOV,SAD, dynamic clamp), so it can monitor the incoming surgecurrent flowing in the clamping circuit. When a surge is present, surgecurrent flows in the transformer primary, producing a canceling signalin the secondary or tapped winding. For a 6,000 volt surge,approximately 5,600 volts will appear briefly across T201 primary. Witha MOV clamp onset of 210 volts, and 3,000 amperes surge currentavailable, the voltage across the MOV may climb to about 400 volts dueto the momentary high surge current flow. A transformer designed forthis application could supply an opposite phase signal of typically 100volts, reducing the surge passed on to the output receptacle or loadfrom 400 volts peak to 300 volts peak or less, making a dramaticimprovement in performance. Transformer couplings greater than 0.5 willresult in greater improvement.

While a MOV (Varistor) is shown in the example, any non-linear clampingcircuit designed for surge suppression use can be substituted for theMOV in this example, with the transformer parameters optimized for theparticular clamping circuit.

FIGS. 2A and 2B show alternative but less preferred present inventionsurge protector circuit arrangements 210 and 220. In these embodiments,the ground line is used for connection of a clamping element, as shown.

FIG. 3 illustrates before and after voltage waveforms for the MOVcircuit at 120 Volts RMS of the present invention device shown in FIG.2. This Figure shows the significant improvement that is possible withthis circuit with the present invention device as compared to thiscircuit without the present invention device, peak surge was 430 volts,while the results with the present invention device was less then 340volts.

The attached waveforms of FIG. 5 show the performance improvement for acircuit using bridge connected diodes and capacitors, such as aredescribed in U.S. Pat. No. 4,870,528, 4,870,534 and 6,728,089. Thepresent invention device results show a surge cap of less than 250volts, while prior art results show a surge cap up to 310 volts.

FIG. 6 shows a circuit diagram of a three phase present inventiondevice. Here device 600 includes three series connected transformers,one for each phase. The three phase service has a typical five line setup, with phase A, phase B and phase C hot lines, a safety ground, and aneutral line. The fixed claming elements RV601, RV602 and RV603 can bereplaced with dynamic clamping circuits as in FIG. 4A, for improvedperformance.

FIG. 7 shows a circuit diagram of one embodiment of a single phasepresent invention surge protector 700 for an input transformer and aseries-connected transformer and 10 amp, 120 vac 60 Hz load. Thecomponents are as follows:

The single phase service 120 vac has a typical three line set up with ahot line, a neutral line, and a safety ground, access via conventionalthree prong plug is assumed for this example. Thus, the presentinvention device 700 has a three-prong male AC plug J701, thatbasically, is a powerline plug for connecting to normal 120 vac 60 Hzpower, although the circuit could also be “hard wired” in a panel-mountapplication or aired circuit having free wires set up for assemblage byan OEM to other components and/or devices.

T701 is a 1200 VA input transformer connected to the hot and neutrallines as shown. T702 is a transformer or autotransformer connected tothe secondary winding of the input transformer, and has a primaryinductance of 20 microhenries, DC resistance of 0.05 ohms, a secondaryinductance of 40 microhenries and a coefficient of coupling of 0.9. R701is a secondary damping resistor across the T702 transformer secondarywinding used to shape the resulting voltage waveform to be consistentwith the clamping circuit response, in the range of 1 to 2 ohms,preferred for this arrangement is 1.5 ohms. RV701 is a Metal OxideVaristor (MOV) or a similar clamping component across the primarywinding of the T702 transformer and the secondary winding of the T701input transformer. RV701 has a nominal clamping onset level of 210 voltspeak, typical of varistors for use with 120 vac power. As shown, it iswired consistent with FIG. 1 above, with the addition of the inputtransformer T701. Comparing this to FIG. 2 components shows the lowerprimary inductance of the series connected transformer by two thirds.This is the result of the leakage inductance (900 microhenries) of theinput transformer T701.

MOVs and SADs (Silicon Avalanche Diodes) have similar clampingcharacteristics for RV701, but MOVs are sacrificial and wear out withuse, while SADs do not wear out up to their maximum rating, but aregenerally available with lower energy or power ratings. A more effectivecircuit would be the circuit of FIG. 4A for RV701 in FIG. 7.

Since the neutral wire is tied to earth ground where the power enters abuilding for 120/240 vac systems as used in the USA, surges can onlyenter a building on the “hot” wires. The transformer (T702) primary istherefore connected to the T701 secondary incoming “hot” wire downstreamfrom the input transformer, and upstream from the clamping circuit(MOV,SAD, dynamic clamp), so it can monitor the incoming surge currentfrom the input transformer flowing to the clamping circuit. When a surgeis present, surge current flows into the input transformer T701, to theseries connected transformer T702 primary, producing a canceling signalin the secondary or tapped winding. For a 6,000 volt surge,approximately 5,600 volts will appear briefly across the primary windingof the input transformer. With a MOV clamp onset of 210 volts, and 3,000amperes surge current available, the voltage across the MOV may climb toabout 400 volts due to the momentary high surge current flow. A seriesconnected transformer, such as transformer T702, designed for thisapplication could supply an opposite phase signal of typically 100volts, reducing the surge passed on to the output receptacle or loadfrom 400 volts peak to 300 volts peak or less, making a dramaticimprovement in performance. The series connected transformers, such astransformer T702, will have a nominal coupling of about 0.6 to about0.95.

While a MOV (Varistor) is shown in the example, any non-linear clampingcircuit designed for surge suppression use can be substituted for theMOV in this example, with the transformer parameters optimized for theparticular clamping circuit.

FIG. 8 illustrates waveform results with the present invention surgeprotector of FIG. 7 utilizing the non-linear surge suppression circuitof FIG. 4A. As shown, peak surge has been reduced by at least 70 voltsin these results.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. A surge protector for an alternating current service, said serviceincluding at least an incoming hot line and an incoming neutral line,which comprises: (a.) an input transformer with input connection meansfor connection to said incoming hot line; (b.) a series connectedtransformer with input connection means for connection to said incominghot line downstream from the input transformer secondary winding, andconnected in series to a non-linear surge suppression circuit, andtherefore having a gross output connection to said non linear surgesuppression circuit, and further having a low impedance signal input tothe secondary of the series connected transformer from said non-linearsurge suppression circuit, and having a surge cancelled hot line outputconnection means; and, (c.) said non-linear surge suppression circuithaving an input connection means from said input transformer secondarywinding, and being connected with said gross output connection means ofsaid transformer, and having means for returning a suppressed surgesignal to said transformer secondary, or tap and having an inputtransformer secondary winding output connection means; wherein thenon-linear surge suppression circuit limits the surge voltage at avoltage above the peak of the power wave voltage, and the seriesconnected transformer senses the surge current and the transformersecondary supplies a signal of opposite phase to the incoming surge atthe output after the clamping circuit, which effectively cancels theresidual surge voltage, rendering the residual surge benign at theoutput.
 2. The surge protector of claim 1 wherein alternating currentservice includes an incoming hot line, an incoming neutral line and asafety ground line, wherein said device further includes a three prongmale alternating current plug at it's upstream end and a three slotfemale alternating current receptacle at it's downstream end.
 3. Thesurge protector of claim 1 wherein said alternating current service issingle phase service, and said service includes an incoming hot line, anincoming neutral line and a safety ground line wherein said seriesconnected transformer has a normal coupling range of about 0.6 to about0.95.
 4. The surge protector of claim 1 wherein said service includes anincoming hot line, an incoming neutral line and a safety ground line ofclaim 1 wherein said non-linear surge suppression circuit includes aclamp circuit selected from the group consisting of a diode bridge, andMOV and an SAD.
 5. The surge protector of claim 1 wherein said inputtransformer is an isolation transformer.
 6. The surge protector of claim1 wherein said input transformer is an step up voltage transformer. 7.The surge protector of claim 1 wherein said input transformer is an stepdown voltage transformer.
 8. The surge protector of claim 1 wherein saidalternating current service is three phase service, and there is atleast one of said series connected transformer and said non-linear surgesuppression circuit.
 9. A surge protector for an alternating currentservice, said service including at least an incoming hot line and anincoming neutral line and an incoming safety ground line, whichcomprises: (a.) an input transformer with input connection means forconnection to said incoming hot line; (b.) a series connectedtransformer with input connection means for connection to said incominghot line downstream from the input transformer secondary winding, andconnected in series to a non-linear surge suppression circuit, andtherefore having a gross output connection to said non linear surgesuppression circuit, and further having a low impedance signal input tothe secondary of the series connected transformer from said non-linearsurge suppression circuit, and having a surge cancelled hot line outputconnection means; and, (c.) said non-linear surge suppression circuithaving an input connection means from the input transformer secondarywinding, and being connected with said gross output connection means ofsaid transformer, and having means for returning a suppressed surgesignal to said transformer secondary, or tap and having an inputtransformer secondary winding output connection means; wherein thenon-linear surge suppression circuit limits the surge voltage at avoltage above the peak of the power wave voltage, and the seriesconnected transformer senses the surge current and the transformersecondary supplies a signal of opposite phase to the incoming surge atthe output after the clamping circuit, which effectively cancels theresidual surge voltage, rendering the residual surge benign at theoutput.
 10. The surge protector of claim 9 wherein alternating currentservice includes an incoming hot line, an incoming neutral line and asafety ground line, wherein said device further includes a three prongmale alternating current plug at it's upstream end and a three slotfemale alternating current receptacle at it's downstream end.
 11. Thesurge protector of claim 9 wherein said alternating current service issingle phase service, and said service includes an incoming hot line, anincoming neutral line and a safety ground line wherein said seriesconnected transformer has a normal coupling range of about 0.6 to about0.95.
 12. The surge protector of claim 9 wherein said non-linear surgesuppression circuit includes a clamp circuit selected from the groupconsisting of a diode bridge, and MOV and an SAD.
 13. The surgeprotector of claim 9 wherein said input transformer is an isolationtransformer.
 14. The surge protector of claim 9 wherein said inputtransformer is an step up voltage transformer.
 15. The surge protectorof claim 9 wherein said input transformer is an step down voltagetransformer.
 16. The surge protector of claim 9 wherein said alternatingcurrent service is three phase service, and there is at least one ofsaid series connected transformer and said non-linear surge suppressioncircuit.